Posterior vaginal wall prolapse (PVP), including enterocele and rectocele, is an enigmatic condition whose pathophysiology is poorly understood. ORWH, NICHD and NIDDK have each identified that female pelvic floor disorders such as PVP are in critical need of pathophysiology research. Competing hypotheses have been proposed relating to the causal roles of endopelvic fascia or levator ani muscle failure. However, data to resolve these conflicts are not available and are needed to establish the relative contributions of fascial and muscular abnormalities to PVP. This study will test the mechanistic hypothesis that the occurrence of PVP is not explained by a single mechanism but involves the interaction between fascial and muscle abnormalities. To test these hypotheses, we will recruit 75 cases with PVP and 75 controls of similar age and race. Aim 1. "Fascia", we will use mid-sagittal MR images made during maximal Valsalva to document the posterior wall location and morphology in 4 regions influenced by fascial support: 1) location of the posterior vaginal apex, 2) length of the posterior vaginal wall, 3) changes in the inclination of the distal vaginal wall, and 4) location of the perineal body. By comparing measurements between cases and controls, we will determine the contributions of abnormalities in each region to the occurrence and size of PVP. Aim 2. "Muscle", we will use multiplanar proton density MR scans to compare 1) presence of visible defects in the levator ani muscles, 2) cross sectional areas of the muscle, as well as measuring and 3) pelvic muscle contraction force during a maximal contraction. Using these data we will determine the contribution of muscular abnormalities. We will then use statistical modeling to determine the relative contributions of fascial versus muscular abnormalities. Aim 3. "Rectocele vs. Enterocele", we will test the strength of association between the 4 fascial and 3 muscle abnormalities and the two types of PVP using general linear modeling. Aim 4, "Biomechanical Modeling", we will use biomechanical analyses of fascia and muscle interactions in computer-based models to investigate patterns of muscle and connective tissue support site failures that lead to PVP. These insights are needed to advance our understanding of disease mechanisms so that we can reduce the 30% recurrence rate of prolapse after surgery, and develop preventative strategies to reduce the need for surgery in 200,000 women each year.